Lossy audio compression is about compromise; quality versus file size and bandwidth. However, for a high quality solution, compression efficiency (though still relevant) can take a back seat. Instead, what we are interested in is support for the format, ease of use (i.e. encoders, taggers, players, gain adjustment tools etc.) and most importantly, audio quality, and in lossy compression terms that means achieving "transparency".

It's worthwhile erring on the side of caution and encoding at marginally higher bit rates than those you might consider transparent. Not all audio is alike and some pieces of music may sound worse than others when compressed.

Note: Transcoding from one lossy format to another seriously degrades audio quality.

The best of the lossy formats are (in alphabetical order):

• AAC (Advanced Audio Coding)
• MP3
• MPC (Musepack)
• OGG (Ogg Vorbis)

Of these we recommend MP3, not because of its quality (as the bit rates we'll suggest pretty much eliminate the quality differences between the codecs) but due to popularity; MP3 is much more broadly supported than the others (though if you are using iTunes and/or an iPod then AAC is a viable choice - note: AAC often has the file suffix M4A or MP4 as well as AAC).

Though AAC is the successor to MP3, the MP3 format is going to be around for a long time and with hard-drives getting ever larger, though we wouldn't recommend it, we can't see anything particularly wrong with encoding MP3s at 320kbps (the highest achievable bitrate). However at this rate WavPack's hybrid lossy encoder and the preprocessor LossyWAV begin to look like better options (for more on this see the Lossless Section).

Choice of Encoder

In terms of quality the choice of encoder is almost as important as the choice of bitrate. We strongly recommend using the latest stable (i.e non beta) release of the LAME encoder (3.98 as of writing this).

To stress the importance of the encoder used, many in the audio community suggest that LAME's 192kbps of 5 years ago probably now equates to today's LAME at 128kbps. Many of the encoders still out there are very poor and should be avoided.

Bitrate: Variable or Constant?

In terms of quality a variable bitrate (VBR) is preferable to a constant bitrate (CBR), unless you encode at 320kbps (which is MP3's ceiling, but this is wasteful and unnecessary). The reason for this is that music varies in complexity and a complex passage making full use of left and right channels will require more bits than a silent or simple mono passage, however CBR will treat these the same. Thus CBR means using a constant bitrate to achieve a variable quality; whereas VBR means using a variable bitrate to achieve a constant quality.

Recommended Setting

To pretty much guarantee transparency we recommend encoding from -V 3 to -V 0 (-V 0 being the maximum VBR setting) in the majority of cases most people will not be able to distinguish between a CD and a LAME encoded MP3 at -V5 (even 128 kbps CBR encodes performed very well in recent tests!). MP3 encoding has improved a lot over the last 10 years!

Lower Bitrates

If space is a problem (e.g. you want a very large number of files on your portable player), then we recommend AAC (encoding with Nero AAC, FAAC or via iTunes if you use it). AAC achieves significantly higher quality at lower bit rates (128 kbps and below), and thus file sizes, than MP3.

We'd like to recommend Musepack; the reasons we can't are: a) development has ceased, and b) it lacks software and hardware support. Still, Musepack is interesting and worth a look at what might have been. You can find out more about it here.

Ogg Vorbis is also very good and open source, but less well supported than MP3.

You can get the latest information on the four codecs mentioned above at Hydrogen Audio.

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